1. Field of the Invention
The present embodiments relate to an organic light emitting diode (OLED) and a method of fabricating the same. Some embodiments relate to an OLED which uses an auxiliary dopant having a higher band gap energy than a host of an emission layer, and preferably having an absolute value of the highest occupied molecular orbital energy level equal to or higher than that of the host, or an absolute value of the lowest unoccupied molecular orbital energy level equal to or lower than that of the host, and thus can facilitate the control of color coordinates, and improve a device's life span, and a method of fabricating the same.
2. Description of the Related Art
Organic light emitting diodes are self emissive displays, which are thin and light, and can have a simple structure fabricated in a simple process, display a high quality picture with a wide viewing angle, implement good motion picture and high color purity, and have electrical characteristics of low power consumption and low driving voltage, which are suitable for mobile displays.
Generally, OLEDs include a pixel electrode, an emission layer disposed on the pixel electrode, and a counter electrode disposed on the emission layer. In such an OLED, when a voltage is applied between the pixel electrode and the counter electrode, holes and electrons are injected into the emission layer and recombined in the emission layer to generate excitons, which transition from an excited state to a ground state, thereby emitting light.
The emission layer of the OLED includes a host and an emitting dopant. The host is generally contained in the emission layer at the highest proportion, and serves to facilitate the fabrication of the emission layer, and to support the structure of the emission layer. Further, when a voltage is applied between the pixel electrode and the counter electrode, carriers are recombined in a host, and the dopant emits light by the excited energy transferred from the host to the dopant. Meanwhile, the emitting dopant is a compound which is fluorescent or phosphorescent, and substantially emits light by excitation by aid of the excited energy transferred from the host.
An auxiliary dopant may be further included in the emission layer to control charge movement in the host, other than the host and the emitting dopant. Conventionally, the auxiliary dopant is formed of a material having an emission spectrum in the same wavelength range as the emitting dopant, or has an energy level limited within an energy level of the host. However, when the energy level of the auxiliary dopant is limited in that of the host, there is a limit to selection of the auxiliary dopant. In addition, it is difficult to control the color coordinates due to interference between energy levels of the host and the dopants, or greater contribution of the auxiliary dopant to the emission than the emitting dopant. The present embodiments overcome the above problems and provide additional advantages as well.